Methods for improving mold quality for use in the manufacture of liquid crystal display components

ABSTRACT

Disclosed herein is a method comprising inspecting a mold for a defect; determining a type of defect present on the mold; sorting the mold by type of defect present; treating the mold with a cleaning process that is suitable to remove the defect; and pressing the mold against a polymeric film to produce a series of defect free light management films; wherein the yield of light management films manufactured from the mold is higher than the yield of light management films that are produced from a comparative mold that has not been treated with the cleaning process.

BACKGROUND

This disclosure relates to methods for improving mold yields for use inthe manufacture of flat panel light management films.

Molds such as, for example, electroforms are generally used formanufacturing light management films such as prism sheets for use inliquid crystalline displays. In general, such light management filmshave at least one microstructured surface that refracts light in amanner effective to enhance the light output of the display. Since thesefilms serve an optical function, it is desirable for the surfacefeatures to be of high quality with no roughness or other defects. Themicrostuctures on the light management films is first generated on amaster, which may be a silicon wafer, glass plate, metal drum, or thelike; and is created by one of a variety of processes such asphotolithography, etching, ruling, diamond turning, or other processes.Since this master tends to be expensive to produce and fragile innature, tooling or molds are generally reproduced off of this master,which in turn serve as the molds from which the light management filmsare mass-produced. These molds can be metal copies grown viaelectroforming processes, or plastic copies formed via molding-typeprocesses.

Molds copied directly from the master (also called a parent mold) arecalled first generation molds (also called daughter molds), copies ofthese first generation molds are called second generation molds, and soon. In general, multiple copies can be made of every mold made at anygeneration, leading to a geometric growth in number of molds with eachgeneration—i.e., a “tooling tree” is produced. Each generation is aninverted image of the previous generation. If the desired final productis a “positive” geometry, then any generation of tooling that is anegative can be used as a mass-production replication mold. If themaster is manufactured as a negative, then any even-generation mold canbe used for mass-production, and vice-versa.

Any mold can have a defect that developed during its manufacture. If thedefect persists in a parent mold, then that defect can be propagated toall subsequent generations of daughter molds and films. In addition, newdefects can appear during the formation of each new generation of amold, and the defect can subsequently be propagated to the futuregenerations if left undetected and uncorrected. Any defect in a moldwill propagate to every copy of that mold, and all subsequentgenerations of molds. Any defect in a mold used for mass-production oflight management films will be replicated in every film produced,resulting in 100% rejection of the films.

There is therefore a need for a process that detects such defects andcorrects molds in order to minimize propagating defects to furthergenerations of molds and light management films, thus improving theiryield. Furthermore, it is desirable for the defect correction procedureto preserve the optical surfaces of the microstructure, and notintroduce any defects such as roughness, pitting, staining, and thelike.

SUMMARY

Disclosed herein is a method comprising inspecting a mold for a defect;determining a type of defect present on the mold; and treating the moldwith a cleaning process comprising one or more cycles that is suitableto remove the defect; wherein the mold does not undergo a degradation incosmetic quality or luminance as a result of being subjected to thecleaning process.

Disclosed herein is a method comprising inspecting a mold for a defect;determining a type of defect present on the mold; sorting the mold bytype of defect present; and treating the mold with a cleaning processthat is suitable to remove the defect without damaging the mold.

Disclosed herein is a method comprising inspecting a mold for a defect;determining a type of defect present on the mold; sorting the mold bytype of defect present; treating the mold with a cleaning process thatis suitable to remove the defect; and pressing the mold against apolymeric film to produce a series of defect free light managementfilms; wherein the yield of light management films manufactured from themold is higher than the yield of light management films that areproduced from a comparative mold that has not been treated with thecleaning process.

Disclosed herein too is a method comprising treating a mold with acleaning process to from a clean mold; wherein the cleaning processcomprises subjecting the electroform to soaking, electrocleaning, awater jet pressurized to at least 15 pounds per square inch,ultrasonication, or a combination comprising at least one of theforegoing cleaning processes; and electroforming a mold using the cleanmold as a template.

DETAILED DESCRIPTION OF FIGURES

FIG. 1, represents a photograph of a defect (prior to ultrasonication),showing a horizontal white line stain (indicated by arrow) in the middleof the circle;

FIG. 2 shows the electroform after removal of the stain; there is nowhite line stain in the circle in FIG. 2 indicating that the defect wasremoved;

FIG. 3 shows a scanning electron microscope image of a 4th generationmold that exhibits no evidence of sub-micron pitting or roughening evenafter 20 full cycles of inspection, cleaning, and mold replication;

FIG. 4 is a schematic depicting how light management films are set-up inorder to measure luminance; and

FIG. 5 is a bar graph showing the relative luminance of light managementfilms made from a 4th generation, second copy mold and a 4th generation,20th copy mold; the graph shows that there is no degradation inperformance even after 18 full cycles of inspection, cleaning and moldreplication.

DETAILED DESCRIPTION

It is to be noted that the terms “first,” “second,” and the like as usedherein do not denote any order, quantity, or importance, but rather areused to distinguish one element from another. The terms “a” and “an” donot denote a limitation of quantity, but rather denote the presence ofat least one of the referenced item. The modifier “about” used inconnection with a quantity is inclusive of the stated value and has themeaning dictated by the context (e.g., includes the degree of errorassociated with measurement of the particular quantity). It is to benoted that all ranges disclosed within this specification are inclusiveand independently combinable.

Disclosed herein are methods to eliminate defects from molds that areused in the manufacture of microstructured films. In one embodiment, themethod comprises first inspecting the mold to detect any defectsfollowed by cleaning the mold using a method designed to remove thedefect. In another embodiment, all molds may be subjected to a singlecleaning process or alternatively to a series of cleaning processes thatcan remove all defects without any inspection. The inspection processand the cleaning process can be performed manually or can be automated.In one embodiment, automated cleaning processes provide a number ofadvantages over manual methods. This includes the provision ofefficient, reproducible processes, which can be more easily controlledand checked than manual methods.

The cleaning process effectively results in the removal of defects fromthe mold thereby leaving the mold capable of being used to producesuccessive generations of additional molds that can be used to producelight management films having an undamaged optical performance.

The cleaning processes are selected so as remove defects from the moldwhile at the same time not damaging the molds. In one embodiment, thecleaning processes are selected such that molds that are subjected to aplurality of cycles of the cleaning process do not undergo microscopicor macroscopic damage. In addition, the cleaning processes are selectedsuch that the mold does not undergo a loss in luminance. A loss inluminance may be attributable to damage undergone during the cleaningprocess, which is undesirable.

The cleaning processes are selected such that a mold subjected to 1 ormore cleaning cycles does not undergo a loss in cosmetic quality oroptical properties. The term cosmetic quality implies that there are noscratches, pits, stains, or the like on the mold after being subjectedto the cleaning process. The term optical properties include reflectanceor luminance from the mold, when the mold is illuminated by a source oflight.

In one embodiment, the cleaning processes are selected such that themolds can be subjected to 1 or more cleaning cycles without undergoingany degradation or loss in luminance. In another embodiment, the moldscan be subjected to 5 or more cleaning cycles without undergoing anydegradation or loss in luminance. In yet another embodiment, the moldscan be subjected to 10 or more cleaning cycles without undergoing anydegradation or loss in luminance. In yet another embodiment, the moldscan be subjected to 20 or more cleaning cycles without undergoing anydegradation or loss in luminance.

The molds can comprise metals, ceramics or polymers. The molds can be inthe form of metal electroforms that are used for manufacturingmicrostructured films. The molds can be flat, curvilinear or cylindrical(e.g., drums). In one embodiment, the cleaning of the mold comprisesprocesses such as soaking the mold in a cleaning solution,electrocleaning, ultrasonication, a high-pressure application ofdeionized (DI) water, or the like, or a combination comprising at leastone of the foregoing processes.

The inspection process includes a visual inspection of the molds toobserve defects and to optionally note their coordinates. A defect is ascratch, stain, pit, or the like, that can scatter visible light andthat has at least one dimension that is greater than or equal to about10 micrometers. This dimension can be measured along the surface of themold or in a direction that is perpendicular to the surface of the mold.Thus a “cleaning process” that introduces at least one defect in a moldor a light management film that is made from the mold can be construedto have damaged the mold. When a child mold (made from a parent mold)has a defect that has at least one dimension of greater than or equal toabout 10 micrometers that was transmitted by the parent mold, it isrejected thereby contributing to a decrease in yield. Similarly, when alight management film contains a defect that has at least one dimensionof greater than or equal to about 10 micrometers that was transmittedfrom the mold, it is rejected thereby contributing to a decrease inyield. A cleaning process can also be construed to have damaged the moldif it changes the surface profile by roughening smooth surfaces offeatures or rounding sharp tips of features, even on a length scale of10 nm. While this damage is invisible to the naked eye or most machinevision systems, it causes diffraction effects and scattering of lightthat degrades the optical quality of the mold and thus the opticalperformance of the films made from the mold.

Defects can be differentiated into two general types of defects, namelyintegral and removable defects. Integral defects are defects that areinherent in the mold. Such integral defects are caused duringmanufacturing or by physical damage that is present on the mold.Examples of these defects are scratches, dashes or separation marks.

Removable defects are superficial defects, which are formed by stains,dust, and other debris. Such defects are termed spiders, blue spots orwhiskers. These defects are caused by the presence of removable debrison the mold. If these defects are not corrected before the parent moldis replicated into daughter molds, all daughter molds will have anintegral defect, which is the geometric replication of the originaldefect. The inspection system is able to distinguish between integraland removable defects and this allows for the eradication of removabledefects from the mold or alternatively, the elimination of those moldsthat have integral defects. In either event, the initial defect will notbe propagated to future generations.

The visual inspection can be conducted in a batch process, in acontinuous process, or in a semi-continuous batch process. A batchprocess is one where each mold is examined manually or where theinspection process is manually assisted (e.g., the molds are placed inthe sample holder manually). A continuous process is one that isautomated such that the molds are mounted on a conveyor belt that movesthe molds into the field of view of the inspection system. Asemi-continuous batch process comprises a manual or manually-assistedinspection or an automated inspection. Both, the visual inspection andthe defect detection may also be automated.

The inspection process can include, for example, a manual inspection, acamera-assisted inspection, or an automated camera inspection. Forexample, the manual inspection process can comprise an unaided visualinspection. In another embodiment, the inspection process can compriseusing visual aids such as line-scan cameras, area cameras, or the like.In still another embodiment, the inspection process comprises usingmicroscopes including light and electron microscopic inspection. Forexample, the light microscopic inspection comprises using objectivelenses of about 5× magnification to about 1000× magnification. Inanother example, the electron microscopic inspection comprises usingscanning electron microscopy (SEM). In yet another embodiment, theinspection can comprise using SEM and energy dispersive x-ray analysis(EDX).

During the inspection process, the mold is illuminated by a light sourceor by a combination of light sources. The light sources are generallyarranged to promote contrast between the defect and the mold, whichfacilitates detection and identification of the defect. The lightsources can include using a flashlight to examine a mold for defects orcan include using a commercially available light source that utilizes upto about ten million candelas for illuminating the mold. In anotherembodiment, a light source that utilizes greater than about ten millioncandelas can be used. In another embodiment, the light sources caninclude structured lights, transition lighting, collimated lightsources, and/or diffuse light sources. In another embodiment, the lightsource can use magnifying light to illuminate and examine the mold. Thelight source can be arranged such that all types of defects areilluminated.

In one embodiment comprising a camera-assisted inspection, a camera ismounted perpendicular to the mold to be inspected. The camera can recordan image of the illuminated mold. The image can be displayed, forexample, on a computer screen. In one embodiment, an operator inspects amagnified, illuminated image displayed on a computer screen anddetermines whether a defect is present. In another embodiment comprisingan automated camera inspection, the image is transferred from the camerato a computer that can analyze the magnified, illuminated image of themold to determine the presence of a defect.

There are several types of removable defects. One example of a removabledefect comprises a particle disposed upon a surface of a mold. Thesetypes of particles include a fiber, a metal chip or a flake, dust, orthe like and are generally embedded in the microstructure, for example,in the grooves between prisms. Other types of removable defects(“whiskers” or “spiders”) can further emanate from a particle disposedupon a surface of a mold, where, for example, long arms project out fromunder the particle. The arms are caused by liquid trapped under thesolid particle that eventually propagates down a groove on the moldsurface due to capillary action. The liquid upon being dried leavesbehind a residue of debris and salts that scatter light. “Whiskers” areanother set of defects and comprise a particle disposed upon a singlesurface groove. The trapped liquid propagates out from the particlealong the single groove forming one or two arms. “Spiders,” on the otherhand, comprise a particle disposed across several surface grooves andhence have a plurality of arms. Another example of a removable defect isa stain, which generally comprises a dried liquid residue. A stain canfurther comprise salts. Such defects are in general caused bycontamination from the air, contaminants in the electroforming baths,contaminants such as greases and oils, inadequate rinsing and cleaningprocedures, or the like.

After the inspection process, the mold can be subjected to a cleaningprocess to remove defects. To effectively and efficiently eliminatedifferent types of removable defects, a suitable cleaning process ismatched to a particular type of removable defect. The inspection processcan determine what type of removable defect is present. Because acleaning process is tailored for a specific type of defect, theremovable defect can be completely removed without wasting a largeamount of time and materials. Exemplary cleaning processes can comprisesoaking, electrocleaning, ultrasonication, a high-pressure applicationof deionized (DI) water, or the like, or a combination comprising atleast one of the foregoing cleaning processes.

A suitable cleaning process can use an effective cleaning solution forremoving a particular type of defect. In one embodiment, a suitablecleaning solution is water. When water is to be used for removing adefect, it is generally desirable to use deionized (DI) water. DI wateris generally used for removing defects that are soluble in water orother polar solvents.

In another embodiment, solvents other than water can be used for soakingthe mold to remove defects. Solvents can be polar or non-polar. In oneembodiment, non-hazardous solvents with low vapor pressure aredesirable. Exemplary polar solvents include ketones (e.g., acetone,methyl ethyl ketone, or the like), alcohols (e.g., methyl alcohol, ethylalcohol, isopropanol, or the like), propylene carbonate, ethylenecarbonate, butyrolactone, acetonitrile, benzonitrile, nitromethane,nitrobenzene, sulfolane, dimethylformamide, N-methylpyrrolidone, or thelike, or a combination comprising at least one of the foregoingsolvents. Exemplary non-polar solvents include benzene, toluene,methylene chloride, carbon tetrachloride, hexane, diethyl ether,tetrahydrofuran, or the like, or combinations comprising at least one ofthe foregoing solvents may also be used. Co-solvents comprising at leastone polar solvent and at least one non-polar solvent may also beutilized.

In another embodiment, cleaning solutions comprising commerciallyavailable general purpose cleaners, such as those used for residentialand industrial purposes may be used for cleaning. These commerciallyavailable cleaners can be further diluted with water or other solventsas desired and used for soaking the mold. In another embodiment,cleaning solutions designed to clean metals, such as nickel or nickelalloy molds, can be used. The chemical composition of the cleaningsolution can vary according to the particular defect to be removed.Suitable cleaning solutions can comprise various cleaning agentsincluding ionic (e.g., anionic, cationic, and zwitterionic) and nonionicdetergents, as well enzymatic cleaning agents. A suitable cleaningsolution can further comprise a non-foaming agent. Suitable cleaningsolutions can comprise an alkaline, acidic or a buffered pH solutionaccording to a particular application of the cleaning solution. In otherembodiments, suitable cleaning solutions can comprise a solvent.Examples of suitable commercially available cleaning solutions includeSIMPLE GREEN®, MICRO-90®, ZYMIT®, LF2100®, SURFACE CLEANSE/930®,STAMPERPREP®, DISCLEAN®, as well as various Alconox products includingLIQUINOX® and CITRANOX®. A suitable cleaning solution can be selectedaccording to the mold, removable defect present, as well as the futureapplication of the mold. For example, STAMPERPREP® is a high alkalinity,low foaming, detergent rich cleaning agent that can be used to clean anickel or nickel alloy mold used in the manufacture of optical media.

The cleaning solution may be added to water or to the organic solvent inan amount of about 2 to about 100 wt %, based on the total weight of thesolution. In another embodiment, the cleaning solution may be added towater or to the organic solvent in an amount of about 5 to about 75 wt%, based on the total weight of the solution. In yet another embodiment,the cleaning solution may be added to water or to the organic solvent inan amount of about 10 to about 60 wt %, based on the total weight of thesolution.

In one embodiment, the cleaning process comprises soaking a mold in anappropriate cleaning solution for about 2 minutes to about 2 hours at adesired temperature. In one embodiment, the cleaning process comprisessoaking the mold in an appropriate cleaning solution for about 15minutes to about 90 minutes. In yet another embodiment, the cleaningprocess comprises soaking the mold in an appropriate cleaning solutionfor about 30 minutes to about 60 minutes.

The temperature of the soaking solution can vary according to theparticular defect and particular mold. In one embodiment, the mold canbe soaked in a cleaning solution maintained at a temperature of about25° C. to about 95° C. In another embodiment, the mold can be soaked ina cleaning solution maintained at a temperature of about 35° C. to about85° C. In yet another embodiment, the mold can be soaked in a cleaningsolution maintained at a temperature of about 45° C. to about 75° C. Inaddition, the cleaning process can comprise a cleaning soak step incombination with other cleaning processes such as mechanical agitation,ultrasonic agitation, or the like.

In one embodiment, in one method of using a cleaning solution to removedefects from the mold, SIMPLE GREEN®, a commercially available cleaningsolution that comprises a combination of organic solvents is added towater and used to soak the mold. The SIMPLE GREEN® is added to water inan amount of about 1 wt % to about 25 wt %, based on the total weight ofthe solution. In another embodiment, the SIMPLE GREEN® is added to waterin an amount of about 3 wt % to about 12 wt %, based on the total weightof the solution. In yet another embodiment, the SIMPLE GREEN® is addedto water in an amount of about 5 wt % to about 10 wt %, based on thetotal weight of the solution. The solution is maintained at roomtemperature during the soaking. The time period for soaking is about oneminute to about thirty minutes. In one embodiment, the time period forsoaking is about three minutes to about fifteen minutes. In anotherembodiment, the time period for soaking is about five minutes to aboutten minutes. This solution can be used to remove a variety of defectsincluding dust, metal particles, dirt, or the like. In addition, thissolution can be used to remove defects caused by oils, greases, saltdeposits, or the like.

In another embodiment, in another method of using a cleaning solution toremove defects from the mold, MICRO-90®, a commercially availablecleaning solution that comprises a mixed buffered solution is added towater and used to soak the mold. The MICRO-90® is added to water in anamount of 2 wt %, based on the total weight of the solution. Thesolution is maintained at room temperature during the soaking. The timeperiod for soaking is about one minute to about four hours. In oneembodiment, the time period for soaking is about fifteen minutes toabout three hours. In another embodiment, the time period for soaking isabout thirty minutes to about two hours. This solution can be used toremove a variety of defects including stains, whiskers, spiders, or thelike. In addition, this solution can be used to remove types of defectsincluding oils, greases, salt deposits, organic contaminates such asstarches and protein-based soils, or the like.

In another embodiment related to soaking, a solution comprisingCITRANOX® and water can be used for removing defects. The solutioncomprising CITRANOX® and water can also be used for neutralizing thesurface of the mold after electrocleaning. For example, the solutioncomprises about 0.5 wt % to about 10 wt % CITRANOX®. In anotherembodiment, the cleaning process comprises using a plurality of rinses,wherein the plurality of rinses can further comprises varyingconcentrations of a cleaning solution. For example, the cleaning processcomprises using a first rinse comprising a cleaning solution having aconcentration of about 5% to about 10% of CITRANOX® and a second rinsecomprising a cleaning solution having a concentration of about 1% toabout 5% of CITRANOX®. In another embodiment, the cleaning processcomprises using a rinse comprising DI water without a cleaning solution.The cleaning process can comprise using a rinse at about 22° C. to about50° C., more specifically about 25° C. to about to 30° C. The cleaningprocess can comprise using a plurality of rinses wherein each rinse isat the same temperature. In another embodiment, the plurality of rinsescomprises using rinses at different temperatures.

As noted above, the cleaning processes can also include electrocleaning(i.e., electrolytic cleaning). Electrocleaning is the process by which aworkpiece is made the anode or the cathode in a bath comprising thecleaning solution. An exemplary cleaning solution is an alkalinecleaning solution. A direct current of about 3 to about 12 volts isapplied to yield a current density of about 10 to about 150 amp/ft²(about 1 to about 15 amp/dm²) of work area. Electrocleaning can beemployed alone or can be preceded by a cleaning soak or some other formof precleaning. In one embodiment, the electrocleaning process isconducted in substantially the same chemical environment as the soakcleaner. In an alternative embodiment, the electrocleaning process isconducted in a different chemical environment as the preceding soakcleaner. For example, an acidic soak can precede an alkalineelectrocleaning process to aid in neutralizing the pH of the acidicsoak.

Anodic electrocleaning can be used on metals, such as ferrous metals. Inthis process, the workpiece is the anode (positive), free electrons aredischarged by the hydroxyl ions to the metal, resulting in a liberationof gaseous oxygen. The oxygen generated at the work surface providescontinuous dynamic agitation, removing and loosening debris therebygreatly aiding the removal of defects. The process also activates themetal surface for subsequent removal of other defects by acid pickling.

Cathodic electrocleaning makes use of a negative charge on theworkpiece. In this process, hydrogen gas is released at the cathode attwice the volume of oxygen at the anode resulting in scrubbing actionand solution agitation. In addition, the negatively charged workpiecerepels negatively charged defects.

Periodic reverse (PR) cleaning can also be employed to combine theeffects of anodic and cathodic electrocleaning. Periodic reversecleaning is a cyclical form of cleaning where the mold to be cleaned isalternatively made the anode or the cathode at intervals of about 4 toabout 10 seconds. This produces hydrogen and oxygen alternatively at thework surface and can be highly effective at removing particular defects.In one embodiment, the final cycle is made anodic to remove any depositsformed during the cathodic cycle.

In one embodiment, in one manner of eliminating defects from the mold, acleaning solution comprising STAMPERPREP® can be used in an electrolyticbath to clean the mold. The mold is used as the cathode. A current ofabout 4 to about 5 amperes per square foot was applied between theelectrodes of the electrolytic bath to clean the mold.

In one embodiment, the cleaning solution comprises STAMPERPREP® in anamount of about 1 wt % to about 5 wt %, based on the total weight of thecleaning solution. In one embodiment, the cleaning solution comprisesSTAMPERPREP® in an amount of about 2 wt % to about 4 wt %, based on thetotal weight of the cleaning solution. In one embodiment, whenSTAMPERPREP® is used in a electrolytic bath, the bath temperature wasmaintained at about 25° C. to about 50° C. In another embodiment, thebath temperature was maintained at about 30° C. to about 40° C. Inanother embodiment, the bath temperature was maintained at about 33° C.to about 38° C. In another embodiment, the cleaning process comprisesusing a current of about four to about five amperes per square foot forabout 1 to about 10 minutes. The cleaning process using the STAMPERPREP®in an electrolytic bath can be conducted for about 2 minutes to about 8minutes.

After electrocleaning, the mold can optionally be subjected to soakingto neutralize any acids or bases left over on the surface of the moldfrom the electrocleaning process. An exemplary formulation for analkaline soak cleaning solution is shown in Table 1. The weight percentsshown in the Table 1 are based on the total weight of the cleaningsolution. Specific formulations and conditions shown in the Table 1 canbe tailored for each application. The formulation of the cleaningsolution and the bath temperature will vary according to the particulardefect to be removed as well as the mold to be cleaned. TABLE 1Component Weight percent (wt %) Sodium metasilicate about 20 to about 60Sodium tripolyphosphate about 6 to about 12 Sodium carbonate about 15 toabout 35 Sodium hydroxide about 10 to about 20 Surfactant(s) about 1 toabout 6 Chelating agents about 1 to about 5

In yet another embodiment, the mold can optionally be subjected to astream of high pressure DI water in order to remove acidic or basictraces after the electrocleaning process.

In still another embodiment, the cleaning process comprises anapplication of high-pressured DI water. In one embodiment, a suitablehigh-pressure DI water apparatus comprises a single jet deliveringapproximately 1200 pulses per minute at a pressure of about 15 poundsper square inch (psi) to about 75 psi. In another embodiment, a suitablehigh-pressure DI water apparatus comprises a plurality of pulsatingjets, for example, about 12 to about 14 jets, operatively connected to adiaphragm pump comprising an input air pressure of, for example, about85 psi or greater and an output pressure of about 45 psi to about 55psi. The mold can be blasted with the water jets for an amount of timeeffective to clean the molds without damaging the mold or reducing theamount of light reflected from the surface of the mold.

A cleaning process that comprises applying high-pressure DI water issuitable to remove defects such as embedded particles including, forexample dust, metal particles, dirt, fibers, or the like. These embeddedparticle defects can also manifest themselves in the form of whiskers,spots, and spiders. In another embodiment, a cleaning process comprisingapplying high-pressure DI water is suitable to remove and/or preventtypes of defects that are soluble in water, such as water solublestains.

In one embodiment, the pressure used in the jets can vary in an amountof about 1 psi to about 75 psi. In another embodiment, the pressure usedin the jets can vary in an amount of about 10 psi to about 50 psi. Inyet another embodiment, the pressure used in the jets can vary in anamount of about 20 psi to about 40 psi.

In another embodiment, the cleaning process comprises ultrasonication.High-intensity ultrasonication that uses a frequency of greater than orequal to about 16 kilohertz (kHz) is based on the interaction of thehigh frequency sound waves with the removable defects on the surface ofthe mold. The defect is removed because of mechanical, thermal andsonochemical effects attributed to generation and collapse ofcavitational bubbles. A cleaning process comprising ultrasonication issuitable to remove defects such as stains, oils, embedded particles,whiskers, spiders, or the like.

In one embodiment, in one manner of cleaning the mold usingultrasonication, water or an organic solvent may be used as the media inwhich the mold is immersed during ultrasonication. In one embodiment,the mold is immersed in a medium comprising organic mineral spirits(OMS). Commercially available cleaning solutions may be added to thewater or to the organic solvents during ultrasonication. The cleaningsolution may be added to water or to the organic solvent in an amount ofabout 2 to about 90 wt %, based on the total weight of the solution. Inanother embodiment, the cleaning solution may be added to water or tothe organic solvent in an amount of about 5 to about 75 wt %, based onthe total weight of the solution. In yet another embodiment, thecleaning solution may be added to water or to the organic solvent in anamount of about 10 to about 60 wt %, based on the total weight of thesolution. Ultrasonication can be conducted for a time period of about 1minute to about 1 hour if desired. In another embodiment,ultrasonication can be conducted for a time period of about 2 minutes toabout 30 minutes if desired.

After treatment of the mold with the appropriate cleaning method, themold can be re-inspected to ensure the removal of the previouslyidentified defect and to further ensure that no new defects have beenintroduced. In the case of a newly discovered defect, the method can berepeated, i.e., identifying the defect and treating with the appropriatecleaning method.

In one embodiment, in one manner of proceeding, a method for removingdefects comprises inspecting the molds, sorting the molds based upon thetype of the defect, subjecting the mold to the appropriate cleaningprocess, and re-inspecting the mold for defects prior to using the moldfor production of light management films or prism sheets.

In another embodiment, in another method of proceeding, a method forremoving defects comprises inspecting the molds, sorting the molds basedupon the type of the defect, subjecting the mold to a series of cleaningprocess to remove multiple types of defects, and re-inspecting the moldfor defects prior to using the mold for production of light managementfilms or prism sheets.

In yet another embodiment, in another method of proceeding, a method forremoving defects comprises excluding the inspecting of the molds. Thisstep comprises subjecting all molds to a series of cleaning processes toremove multiple types of defects and then using the mold for productionof light management films or prism sheets. Inspection is thus avoided.

In another embodiment, the cleaning process comprises rinsing anddrying. A cleaning process comprising rinsing and drying is suitable toremove defects such as residual salts on the mold remaining from theelectroforming bath. In the absence of rinsing and drying, the residualsalts can potentially re-concentrate on the surface of the moldresulting in stains.

After the mold is subjected to the inspection process and/or thecleaning process, it can be used to press a generation of lightmanagement films or alternatively it can be used as a template tomanufacture a generation of molds. The methods described above aretherefore advantageous in that defects are not transferred from onegeneration of molds to the next. Cleaning the molds also permits defectfree light management films to be manufactured thereby improving theyields of the manufacturing process.

The following examples, which are meant to be exemplary, not limiting,illustrate compositions and methods of cleaning some of the moldsdescribed herein.

EXAMPLES Example 1

This example demonstrates a series of cleaning processes that can beused for eliminating defects from a metal electroform without areduction in optical quality of the mold. As will be seen below, thecleaning process comprises subjecting the electroform to a series ofprocess that facilitate removal of the defects from the surface of theelectroform. After each cleaning step, the electroform is subjected to arinse in DI water to remove any traces of acid or base. Following eachrinse, the electroform is once again subjected to inspection todetermine if all defects are eliminated. When all of the defects areeliminated, the cleaning process is stopped.

In this example, a manufactured electroform is first subjected to aninitial cleaning. The electroform was peeled from a master and subjectedto an initial cleaning comprising a DI water rinse.

The electroform is then subjected to a one-minute DI water rinse using ahigh-pressure jet under ambient temperature. The electroform is thendried and inspected for defects. If a defect is found to be present,electrocleaning is performed at 10.5 volts with about 4 to 5 amps persquare foot using STAMPERPREP® cleaning solution for about five minutes.Following the electrocleaning, the electroform is rinsed in DI water.The electroform is then soaked in a 2% Citranox solution for 3 minutesfollowed by another rinse in DI water. The electroform is then dried andre-inspected. If defects are still found to be present, the electroformis soaked in 1% MICRO-90® solution for 30 minutes following which it wasinspected again. If the defect is still present, then the electroform issoaked in the MICRO-90® solution for up to 2 hours.

Example 2

This example was conducted to demonstrate the removal of a defect froman electroform when using ultrasonication as part of a cleaning process.FIG. 1 and FIG. 2 depict photographs showing the defect before and afterthe cleaning process respectively. FIG. 1, which represents a photographof the defect, shows a horizontal white line stain in the middle of thecircle. The circle indicates the location of the defect. The electroformwas then subjected to ultrasonication to remove the defect.

A 5 wt % solution of MICRO-90® in water (based on the total weight ofthe solution) was used as the media for ultrasonication. Ultrasonicationwas conducted for a period of 5 minutes at room temperature. Followingultrasonication, the defect was removed. FIG. 2 shows the electroformafter removal of the stain. There is no white line stain in the circlein FIG. 2 indicating that the defect was removed.

Example 3

This example was performed to demonstrate the lack of damage to moldssubjected to the selected cleaning processes. A third-generation moldwas used to produce 20 children, undergoing the inspection, cleaning andreplication process each time. To clean the electroforms for use as aparent for manufacturing a series of future generations of molds, or foruse as a template to make light management films, the molds weresubjected to a series of steps as detailed in Example 1. After eachcleaning step, the mold was subjected to inspection. Inspections wereconducted visually using a flashlight or a camera. Automated inspectionswere also performed on the mold after some of the cleaning steps.

The 20^(th) child of this third generation mold, itself a fourthgeneration mold, was then examined using scanning electron microscopy.An image of the mold is shown in the FIG. 3. After going through 20 fullcycles of inspection, cleaning and replication, the third generationparent had not propagated any sub-micron roughness or pitting onto its20^(th) child, indicating that these cleaning processes can clean themold while at the same time preserving it for long term use.

Example 4

This example demonstrates the performance of two batches of lightmanagement films manufactured from sibling fourth-generation molds. Onebatch of light management films was made from a mold that was the secondchild to come off its third generation parent. The other batch was madefrom a mold that was the 20^(th) child to come off the same thirdgeneration parent. The example shows that light management films displayalmost identical relative luminance characteristics despite the factthat the parent third generation mold was subjected to 18 cycles ofcleaning, replication and inspection between the production of thesecond child mold and the 20^(th) child mold.

The luminance of the two light management films was tested as follows. Abottom diffuser is placed in a backlight with an inverter. The bottomdiffuser is a D120® commercially available from Tsujiden Co. Ltd, whilethe backlight is a LG Philips LP121X1® backlight having a single coldcathode fluorescent light (CCFL) as the source of illumination. Theinverter is a LS390® inverter commercially available from Taiyo Yuden. Alight management film in the vertical configuration is placed over thebottom diffuser. A light management film in the horizontal configurationis placed over the vertical light management film. In order to make theluminance measurement on a particular light management film, the lightmanagement film was cut into 2 portions. One portion was used in thevertical configuration and the other portion was used in the horizontalconfiguration. The configurations are shown in the FIG. 4.

Several thermocouples monitor the temperature of the backlight. Aftereach set of samples is installed in the activated backlight, the systemis allowed to equilibrate until the backlight temperature remains steadyto within 0.1 degrees over the course of 5 minutes. After the system isequilibrated, a SS220® Display Analysis System commercially availablefrom Microvision is used to measure 13 point luminance uniformity andthe view angle at the center point. Performance is measured in “relativeluminance” units compared to a brightness enhancing film (BEF2) filmmanufactured by 3M.

The data for both copies of light management films is shown in the FIG.5. From this figure it can be seen that both films have a relativeluminance of about 106 units. The films from the 2^(nd) copy had anaverage normalized luminance of 106.72% with a standard deviation of0.15%, while the films from the 20_(th) copy had an average normalizedluminance of 106.76% with a standard deviation of 0.16%, which makesthem statistically equal at a 95% confidence limit. In other words, evenafter 18 inspection, cleaning, and replication cycles, there was nodecrease in quality of the film produced from the molds.

From the above examples, it may be seen that several cleaning processescan be used sequentially to remove defects. Alternatively a singlecleaning process can be used to remove defects and increase yield. Theexample shows that light management films display almost identicalrelative luminance characteristics despite the fact that the parentthird generation mold was subjected to 18 cycles of cleaning,replication and inspection between the production of the second childmold and the 20^(th) child mold.

In an advantageous embodiment, a parent mold that has been subjected tothe inspection and/or cleaning process can be used as a template tocreate a first generation of daughter molds. A mold from the firstgeneration of daughter molds can be used to create a second generationof daughter molds. In one embodiment, several molds from the firstgeneration of daughter molds can be used to create a plurality of secondgenerations of daughter molds. In this manner a tooling tree thatcomprises a plurality of generations of molds that is defect free can becreated.

In one embodiment, by using a manufacturing method that comprises theaforementioned inspection and/or cleaning processes, the yield of moldsin a given tooling tree of manufactured molds can be improved by about10 to about 90% over the yields from those manufacturing methods that donot involve inspection and/or cleaning processes. In other words, if amold from a first generation of daughter molds is subjected to theinspection and/or cleaning process and is used as a template tomanufacture additional molds for a second generation of daughter molds,then the yield of second generation daughter molds can be increased inan amount of about 10 to about 90% over another comparative secondgeneration of daughter molds manufactured from a comparative firstgeneration daughter mold that has not been subjected to the cleaningprocess.

In another embodiment, the yield of molds in a given tooling tree can beimproved by about 30 to about 85% over the yield obtained from othercomparative manufacturing methods that do not involve inspection and/orcleaning processes. In yet another embodiment, the yield of molds in agiven tooling tree can be improved by about 40 to about 80% over theyield obtained from other comparative manufacturing methods that do notinvolve inspection and/or cleaning processes. In yet another embodiment,the yield of molds in a given tooling tree can be improved by about 45to about 75% over the yield obtained from other comparativemanufacturing methods that do not involve inspection and/or cleaningprocesses.

Similarly, the yield of light management films or prism sheets can beimproved by about 20 to about 90% over the yield from a comparativemethod that does not involve inspection and/or cleaning processes forthe molds. In one embodiment, the yield of light management films orprism sheets can be improved by about 25 to about 75% over the yieldfrom a comparative method that does not involve inspection and/orcleaning processes for the molds. In one embodiment, the yield of lightmanagement films or prism sheets can be improved by about 30 to about50% over the yield from a comparative method that does not involveinspection and/or cleaning processes for the molds.

In one embodiment, a mold that is subjected to the cleaning process canundergo a reduction in the number of defects present in the mold. Thereduction in the number of defects can be at least about 1% over acomparative mold that is not subjected to the cleaning process. In oneembodiment, the reduction in the number of defects can be at least about2% over a comparative mold that is not subjected to the cleaningprocess. The reduction in the number of defects can be at least about 5%over a comparative mold that is not subjected to the cleaning process.In one embodiment, the reduction in the number of defects can be atleast about 10% over a comparative mold that is not subjected to thecleaning process. In another embodiment, the reduction in the number ofdefects can be at least about 50% over a comparative mold that is notsubjected to the cleaning process. In yet another embodiment, thereduction in the number of defects can be at least about 100% over acomparative mold that is not subjected to the cleaning process.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method comprising: inspecting a mold for a defect; determining atype of defect present on the mold; sorting the mold by type of defectpresent; treating the mold with a cleaning process that is suitable toremove the defect; and pressing the mold against a polymeric film toproduce a series of light management films; wherein the yield of defectfree light management films manufactured from the mold is higher thanthe yield of light management films that are produced from a comparativemold that has not been treated with the cleaning process.
 2. The methodof claim 1, wherein the inspecting is conducted under light sources thatincrease contrast between the defects and the mold.
 3. The method ofclaim 1, further comprising inspecting the mold after the cleaning todetermine if the defect is removed.
 4. The method of claim 1, whereinthe inspecting the mold comprises using a camera to inspect the mold. 5.The method of claim 4, wherein the camera is a line-scan camera or anarea camera.
 6. The method of claim 1, wherein the inspecting the moldcomprises using a scanning electron microscope and/or energy dispersivexray analysis to inspect the mold.
 7. The method of claim 1, wherein thecleaning process comprises soaking the mold in deionized water.
 8. Themethod of claim 1, wherein the cleaning process comprises soaking themold in an organic solvent.
 9. The method of claim 1, wherein thecleaning process comprises subjecting the mold to ultrasonication. 10.The method of claim 9, wherein the ultrasonication is conducted inwater, in organic solvents, or in a combination comprising water andorganic solvents.
 11. The method of claim 1, wherein the cleaningprocess comprises subjecting the mold to electrocleaning.
 12. The methodof claim 11, wherein the electrocleaning is conducted in water, inorganic solvents, or in a combination comprising water and organicsolvents.
 13. The method of claim 1, wherein the cleaning processcomprises subjecting the mold to a water jet pressurized to at least 15pounds per square inch.
 14. The method of claim 1, wherein the cleaningprocess comprises subjecting the mold to soaking, electrocleaning, awater jet pressurized to at least 15 pounds per square inch,ultrasonication, or a combination comprising at least one of theforegoing cleaning processes.
 15. The method of claim 7, furthercomprising adding a cleaning agent to the deionized water.
 16. Themethod of claim 15, wherein the cleaning agent comprises an ioniccleaning agent, a non-ionic cleaning agent, an enzymatic cleaning agent,or a combination comprising at least one of the cleaning agents.
 17. Themethod of claim 15, wherein the cleaning agent further comprises anon-foaming agent, an alkaline pH solution, an acidic pH solution, abuffered pH solution, or a combination comprising at least one of theforegoing.
 18. The method of claim 1, wherein the mold is anelectroform.
 19. The method of claim 1, wherein the mold that issubjected to the cleaning process has a reduction in defects in anamount of about 1 to about 100% over a comparative mold that has notbeen subjected to the cleaning process.
 20. The method of claim 1,further comprising using the mold after being treated with the cleaningprocess as a template to produce a first generation of molds.
 21. Themethod of claim 1, further comprising using the mold to produce atooling tree, wherein the tooling tree comprises a plurality ofgenerations of molds.
 22. The method of claim 1, wherein the yield ofmolds for the tooling tree is about 10 to about 90% greater than acomparative tooling tree manufactured by a process that does notcomprise an inspection and/or cleaning processes.
 23. A methodcomprising: treating a mold with a cleaning process to form a cleanmold; wherein the cleaning process comprises subjecting the electroformto soaking, electrocleaning, a water jet pressurized to at least 15pounds per square inch, ultrasonication, or a combination comprising atleast one of the foregoing cleaning processes; and electroforming a moldusing the clean mold as a template.
 24. The method of claim 23, furthercomprising inspecting the mold under visible light.
 25. The method ofclaim 23, wherein the mold is an electroform.
 26. The method of claim23, wherein the mold that is treated to the cleaning process has areduction in defects in an amount of about 1 to about 100% over acomparative mold that has not been subjected to the cleaning process.27. A method comprising: inspecting a mold for a defect; determining atype of defect present on the mold; sorting the mold by type of defectpresent; and treating the mold with a cleaning process that is suitableto remove the defect without damaging the mold.
 28. The method of claim27, wherein the cleaning process comprises soaking the mold in asolvent, electrocleaning the mold, blasting the mold with a water jetpressurized to at least 15 pounds per square inch, ultrasonication, orsoaking the mold in an ionic cleaning agent, a non-ionic cleaning agent,an enzymatic cleaning agent or a combination comprising at least one ofthe cleaning agents.
 29. A method comprising: inspecting a mold for adefect; determining a type of defect present on the mold; and treatingthe mold with a cleaning process comprising one or more cycles that issuitable to remove the defect; wherein the mold does not undergo adegradation in cosmetic quality or luminance as a result of beingsubjected to the cleaning process.
 30. The method of claim 29, whereinthe cleaning process comprises 5 or more cycles.
 31. The method of claim29, wherein the cleaning process comprises 10 or more cycles.
 32. Themethod of claim 29, wherein the inspecting is conducted under lightsources that increase contrast between the defects and the mold.
 33. Themethod of claim 29, further comprising inspecting the mold after thecleaning to determine if the defect is removed.
 34. The method of claim29, wherein the inspecting the mold comprises using a camera to inspectthe mold.
 35. The method of claim 29, wherein the cleaning processcomprises soaking the mold in deionized water.
 36. The method of claim29, wherein the cleaning process comprises soaking the mold in anorganic solvent.
 37. The method of claim 29, wherein the cleaningprocess comprises subjecting the mold to ultrasonication.
 38. The methodof claim 29, wherein the cleaning process comprises subjecting the moldto electrocleaning.
 39. The method of claim 29, wherein the cleaningprocess comprises subjecting the mold to soaking, electrocleaning, awater jet pressurized to at least 15 pounds per square inch,ultrasonication, or a combination comprising at least one of theforegoing cleaning processes.
 40. The method of claim 29, wherein themold is an electroform.
 41. A film manufactured by the method ofclaim
 1. 42. A mold manufactured by the method of claim 23.